/*
 * Copyright 2007 ZXing authors
 * 
 * Modified by John Ahlroos 2011
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package fi.jasoft.qrcode.zxing;

/**
 * <p>
 * Encapsulates a QR Code's format information, including the data mask used and
 * error correction level.
 * </p>
 * 
 * @author Sean Owen
 * @author John Ahlroos
 * @see DataMask
 * @see ErrorCorrectionLevel
 */
final class FormatInformation {

    private static final int FORMAT_INFO_MASK_QR = 0x5412;

    /**
     * See ISO 18004:2006, Annex C, Table C.1
     */
    private static final int[][] FORMAT_INFO_DECODE_LOOKUP = {
            { 0x5412, 0x00 }, { 0x5125, 0x01 }, { 0x5E7C, 0x02 },
            { 0x5B4B, 0x03 }, { 0x45F9, 0x04 }, { 0x40CE, 0x05 },
            { 0x4F97, 0x06 }, { 0x4AA0, 0x07 }, { 0x77C4, 0x08 },
            { 0x72F3, 0x09 }, { 0x7DAA, 0x0A }, { 0x789D, 0x0B },
            { 0x662F, 0x0C }, { 0x6318, 0x0D }, { 0x6C41, 0x0E },
            { 0x6976, 0x0F }, { 0x1689, 0x10 }, { 0x13BE, 0x11 },
            { 0x1CE7, 0x12 }, { 0x19D0, 0x13 }, { 0x0762, 0x14 },
            { 0x0255, 0x15 }, { 0x0D0C, 0x16 }, { 0x083B, 0x17 },
            { 0x355F, 0x18 }, { 0x3068, 0x19 }, { 0x3F31, 0x1A },
            { 0x3A06, 0x1B }, { 0x24B4, 0x1C }, { 0x2183, 0x1D },
            { 0x2EDA, 0x1E }, { 0x2BED, 0x1F }, };

    /**
     * Offset i holds the number of 1 bits in the binary representation of i
     */
    private static final int[] BITS_SET_IN_HALF_BYTE = { 0, 1, 1, 2, 1, 2, 2,
            3, 1, 2, 2, 3, 2, 3, 3, 4 };

    private final ErrorCorrectionLevel errorCorrectionLevel;
    private final byte dataMask;

    private FormatInformation(int formatInfo) {
        // Bits 3,4
        errorCorrectionLevel = ErrorCorrectionLevel
                .forBits((formatInfo >> 3) & 0x03);
        // Bottom 3 bits
        dataMask = (byte) (formatInfo & 0x07);
    }

    static int numBitsDiffering(int a, int b) {
        int diff = a ^ b;

        // Count bits set quickly with a series of lookups:
        return BITS_SET_IN_HALF_BYTE[diff & 0x0F]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 4 & 0x0F)]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 8 & 0x0F)]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 12 & 0x0F)]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 16 & 0x0F)]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 20 & 0x0F)]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 24 & 0x0F)]
                + BITS_SET_IN_HALF_BYTE[(diff >>> 28 & 0x0F)];
    }

    /**
     * @param maskedFormatInfo1
     *            format info indicator, with mask still applied
     * @param maskedFormatInfo2
     *            second copy of same info; both are checked at the same time to
     *            establish best match
     * @return information about the format it specifies, or <code>null</code>
     *         if doesn't seem to match any known pattern
     */
    static FormatInformation decodeFormatInformation(int maskedFormatInfo1,
            int maskedFormatInfo2) {
        FormatInformation formatInfo = doDecodeFormatInformation(
                maskedFormatInfo1, maskedFormatInfo2);
        if (formatInfo != null) {
            return formatInfo;
        }
        // Should return null, but, some QR codes apparently
        // do not mask this info. Try again by actually masking the pattern
        // first
        return doDecodeFormatInformation(maskedFormatInfo1
                ^ FORMAT_INFO_MASK_QR, maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR);
    }

    private static FormatInformation doDecodeFormatInformation(
            int maskedFormatInfo1, int maskedFormatInfo2) {
        // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
        int bestDifference = Integer.MAX_VALUE;
        int bestFormatInfo = 0;
        for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.length; i++) {
            int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
            int targetInfo = decodeInfo[0];
            if (targetInfo == maskedFormatInfo1
                    || targetInfo == maskedFormatInfo2) {
                // Found an exact match
                return new FormatInformation(decodeInfo[1]);
            }
            int bitsDifference = numBitsDiffering(maskedFormatInfo1, targetInfo);
            if (bitsDifference < bestDifference) {
                bestFormatInfo = decodeInfo[1];
                bestDifference = bitsDifference;
            }
            if (maskedFormatInfo1 != maskedFormatInfo2) {
                // also try the other option
                bitsDifference = numBitsDiffering(maskedFormatInfo2, targetInfo);
                if (bitsDifference < bestDifference) {
                    bestFormatInfo = decodeInfo[1];
                    bestDifference = bitsDifference;
                }
            }
        }
        // Hamming distance of the 32 masked codes is 7, by construction, so <=
        // 3 bits
        // differing means we found a match
        if (bestDifference <= 3) {
            return new FormatInformation(bestFormatInfo);
        }
        return null;
    }

    ErrorCorrectionLevel getErrorCorrectionLevel() {
        return errorCorrectionLevel;
    }

    byte getDataMask() {
        return dataMask;
    }

    public int hashCode() {
        return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
    }

    public boolean equals(Object o) {
        if (!(o instanceof FormatInformation)) {
            return false;
        }
        FormatInformation other = (FormatInformation) o;
        return this.errorCorrectionLevel == other.errorCorrectionLevel
                && this.dataMask == other.dataMask;
    }

}
